Three years ago, geoscientist Robert D’Anjou climbed into an inflatable raft and navigated to the deepest spot in Lake Liland in northern Norway. He and collaborators dropped a coring device about 45 feet down and began to drill, in what would turn out to be a quixotic scientific search for the ancient remains of human excrement.

D’Anjou, a graduate student at the University of Massachusetts Amherst, didn’t start out with scatalogical interests. He was interested in reconstructing ancient climate records by studying layers of sediment.

But he realized that many of the indirect markers that scientists used to look for past climate changes were intricately linked to human influence. Scientists often search for pollen, for example, but changes in plant life can be a sign not only of climate change, but agriculture. Similarly, erosion could reflect changes caused by climate fluctuations—droughts that killed plants that held soil in place, for example—but could also be caused by the introduction of livestock or changing land use.

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So he began examining the sediments in detail, and found that coprostanols, molecules produced in human guts as people digest cholesterol, could be used in combination with other more commonly used molecular remains to look at the interactions between humans and their environments. The results, published Monday in the Proceedings of the National Academy of Sciences, suggest a possible new approach to understanding the relationship between prehistoric humans and their environment. Still, D’Anjou has kept a sense of humor about the whole project.

“You can’t take yourself too seriously. I studied Viking poop,” D’Anjou said. “It’s hilarious, but at the same time you’ve got to look at it kind of pragmatically. ... People have been recording their stories throughout history in the most unlikely of places—in their poop.”

The researchers found no evidence in the sediments from the bottom of the Norwegian lake of human presence on its shores before about 2,300 years ago. There were molecules more commonly found in the excrement of other mammals, but the authors interpreted that background level as indicative of moose or deer, rather than livestock.

Then, about 2,300 years ago, there was a spike in molecules that indicated widespread burning, suggesting fire may have been used to clear land in the area. That was followed by a spike in the remains of human fecal matter, which would have accumulated as rains washed human excrement into the lake. D’Anjou and colleagues found molecular remnants that signaled the rise and decline of settlement around the lake, with the fecal patterns mirroring those found in plant matter or remnants of burning. And they found a decline in the ancient remains of human poop during a time that might be attributed to the spread of the plague.

Francesco Berna, a research assistant professor at Boston University who studies prehistoric settlement by searching for traces of the fires they set, said that he hopes the technique can be expanded to more sites. Although it is unlikely they will be preserved except in special conditions, such as beneath a lake, he hopes to be able to find such biomarkers at much older sites.

In D’Anjou’s study, “after humans start to occupy, you have a clear signature of their presence in the lake,” Berna said. “It is very well done because it’s a good situation to analyze, as we have other historical data ... so this is a good landmark paper to say—look when it works, it works.”

Overall, D’Anjou hopes that the work will provide a valuable tool to archeologists and geologists trying to understand the ancient climate and the way that humans both responded to and shaped the environment.